Synchronizing system



H. c. REssLER 2,266,802

SYNCHRONIZING SYSTEM y Filed N`ov. 6, 19.39 2 Sheets-Sheet l Dec. 23, 1941.

ATTORNEY Dec. 23, 1941. H. c. REssLE-R 2,266,802

SYNCHROYNI Z ING SYSTEM Filed NOV. 6, 1959 2 Sheets-Sheet 2 F/efQL/EA/cy FREQUENCY /QEQUEA/cr ATTO R N EY Patented Dec. 23, 1941 SYNCHRONIZING SYSTEM Hugh C. Ressler, West Brighton, Staten Island,

N. Y., assgnor to Radio Inventions, Inc., New

York, N. Y., a corporation of New York Application` November 6, 1939, Serial No. 303,087

(Cl. P18-69.5)

Claims.

The present invention concerns synchronizing systems and, in particular, a system for synv chronizing motor-driven `facsimile recorders by means of a substantially pure sine wave signal harmonically related to, and derived from, a series of periodic impulses.

One object of the present invention is to derive a series of periodic impulses from a'series of periodic impulses of lower period.

Another object of this invention is to derive a substantially pure sine wave signal from a series of periodic impulses.

Another object is to derive substantially pure sine wave harmonic signals from lower frequency periodic signals by means of aperiodic circuits.

Still another object is to provide highly eflicient harmonic signal deriving means by means of inexpensive and practical circuits.

These and other objects of the present inven-l tion will be evident from the detailed description of the various figures of the drawings.

In the past, synchronizing impulses have been utilized in a number of ways to control facsimile receiving apparatus. One system is described in the patent entitled Facsimile synchronizing system issued March l1, 1941, and bearing No. 2,234,919. In this system, a tuning fork acts to lter a desired frequency component from a received synchronizing impulse and is in turn synchronized by the filtered component. Another system is shown in the copending application entitled Facsimile synchronizing system filed on September 14, 1939, and bearing Serial Number 294,868. A system is shown in which the fundamental frequency of the synchronizing impulse is first recaptured and this fundamental frequency is. multipled to produce the desired synchronizing frequency.

In the present system, signals of the desired synchronizing frequency are derived by one or more selective frequency multiplications of lthe received impulse. The amplitude of signal is limited at one or more points and the selective multiplication is carried on in aperiodic circuits by means4 of bridge type selective feed-back circuits. By adjusting the selective system in such a way that undesired signal components on either side of the desired component tend to equalize a considerable increase in stability is realized.

In the drawings:

Fig. 1 shows a facsimile receiver circuit embodying one form of the present invention.

Figs. 2, 3, 4, 5, 6, 7, 8 and 9 show various curves and diagrams useful in explaining the operation of the invention.

Fig. 10 shows a block diagram of the components of one form of the invention.

In Fig. 1 is shown one form of the present invention included in a facsimile receiver. The receiver includes a conventional carrier wave re.

ceiver 3 connected to antenna I and ground 2. Receiver 3 feeds a signal separator 4 which in turn feeds both recording and synchronizing devices. The recording signals after separation are rectified and amplified in the rectifier and amplier unit 5 and fed to recording stylus 1, in order to record on a record sheet attached to or passing over drum 6. Drum 6 is driven by synchronous motor 8 which receivesits power from power amplifier 65. The desired speed" relation between motor and drum speeds is secured by means of gear box 8. Since the components so far described are not directly the subject of this invention, they are shown in block diagram, indicating that alterations or substitutions may be made consistent with the synchronizing system to be described. n

The present invention concerns the circuits for transforming synchronizing impulses into desired substantially steady signals. These circuits are shown connected between one output of signal separator 4 and the input to power amplifier 65. In the preferred form shown, these circuits include the limiter-amplifier stage utilizing tube I I, the selective feed-back stage utilizing tube 25, thesecond limiter-amplifier stage utilizing tube 40 and the second selective feed-back stage utilizing tube 49, which last stage feeds power amplier B5.

synchronizing impulses from signal separator 4 are applied to grid I3 and diode plate I4 of tube I I thru the series resistor I0 and across grid leak resistor 9, one end of which is connected to ground 2. Tube II also includes cathode I5 connected to ground 2 and plate I2 energized from plate voltage source I'I thru load resistor I6. The synchronizing signals received from the signal separator 4 are relatively widely separated impulses, such as impulses of to second duration 1/3.3 second apart, as shown in Fig. 5. These impulses are limited by the action of diode plate I4 to a predetermined level as shown by the dotted line in Fig. 5, in order to supply essentially constant amplitude impulses to grid I3 in the presence of fading, etc. This leveling takes place due to the fact that when the positive voltage due to the impulses at plate I4 causes plate I4 to draw current, the impedance between plate I4 and cathode I5 becomes very low and any further increase in.

instantaneoussignal is dissipated in resistor I0.

` operates across grid resistor 'numberof the harmonics are represented by the vertical lines a, b, c, d and e in Fig. 2. The selective feed-back amplifier utilizing tube 25 selects one of these harmonics c. Tube 25 includes cathode 24, control grid 26, screen grid 21, suppressor grid 23 and plate 29. Impulses from tube I'I appearing across load resistor I6 are applied to grid 26 from a tap 2l on grid resistor 2li, which is coupled to load resistor I6 thru coupling condenser I9. A grid bias battery 22 is connected between grid resistor 20 and cathode 24. Plate 29, is loaded by resistor 30 and energized from plate voltage supply I1. Between plate 29 and grid 26 is connected a selective circuit dncluding resistors 34, 35 and 59 and condensers 32, 33 and 36 connected to ground 2 at the junction between resistor 59 and condenser 36 and to plate 29 thru blocking condenser 3i. This selective circuit transmits all frequencies except frequency nj* as determined by the equation Where R=R34=R35=2(R59) and quency of desired component c of Fig. 2, as shown by selectivity curve g, lthat the resulting components are as shown in Fig. 3 where m is the selected desired component and h, k, n and p are the attenuated undesired components. It will be noted that the adjacent undesired component k is greater than the adjacent undesired component n on the other side of m, which in practice produces a condition in which component 7c is relatively more troublesome than n. If, however, the bridge is balanced to be selective, as shown at f of Fig. 2 to one side of c, so that undesired components b and d are made more nearly equal, as shown at t and vin Fig. 4,`the interference due to undesired components is reduced and the stability of the system is increased. This shifting of theA selectivity curve toward the smaller amplitude or higher frequency undesired component has also been found to produce greater equality of spacing of the desired harmonic component in time especially'near its zero voltage points.

The frequency multiplied synchronizing impulse signals are limited by tube 40 in which diode plate 43 in conjunction with cathode 44 to limit signals of more than a predeterminedamplitude. When the predetermined amplitude is reached, the signal is limited by series resistor 39 and the limited signal appears on grid 42. The signals resulting from the first multiplicationappearing at plate 29 are applied 38 to one end of resistor 39 thru coupling condenser 31. The limited signals applied to grid 42 are amplified by tube 40 and appear on plate 4I and across plate load resistor 2,266,309 I Y j :2., me end or which is connected tu pim my ry 1. I

A desired range of harmonics of the amplifiedlimited signals are applied across resistor 4l thru -blocking condenser 41. Condenser" is made small enough to substantiallyllimit the fundamental components of the plate voltage signals thus increasing the ratio of desired harmonic components to the lower frequency components resulting in signals of the general form shown t in Fig. 7.

A portion of these harmonic accentuated signals are applied to the second selective amplifier tube 49 by connecting grid 5| to a tap 46' on resistor 46. Tube 49 includes a cathodel 50, control grid 5I, screen grid 52, suppressor grid 53 and plate 54. Tube 49 is made to function as a selective amplifier by connecting a selective feedback circuit between plate 54 and grid 5I comprising resistors 58, 60 and 6I and condensers 56, 51 and 62 coupled to plate 54 thru blocking condenser and grounded at junction of resistor 60 and condenser 62. The circuit is selective at a new harmonic frequency f', the amplifier operating at full gain at this frequency. At frequencies higher and lower than f', the circuit feeds back a degenerative voltage to grid 5 I, reducing the gain of the stage at these frequencies. As before, the circuit is made to be selective at a slightly higher frequency than the frequency of the desired harmonic component which it is to select in order to minimize the disturbing effect of undesired adjacent harmonics. The nally selected harmonic will have a substantially pure sine wave form. This harmonic is reproduced across plate load resistor 63, energizing plate 54 from battery l1. This desired harmonic is then applied to power amplifier 65, thru blocking condenser 64, where it is amplified and utilized to drive motor 9 connected by leads 66 and 61.

Figs. 5, 6, '1, 8 and 9 show the evolution of the final steady sine wave synchronizing tone of Fig. 9 from the transmitted synchronizing impulse of Fig. 5. As described above, the received synchronizing impulses of Fig. 1 are limited as shown by the dotted line in the limiter tube il. These impulses may be, for instance, V second long separated l/3.3 second. Selective amplifier 25 generates a 20 cycle damped wave as shown inv Fig. 6. When this Wave is limited by tube 40 at the dotted line of Fig. Grthe 20 pulses per second shown in Fig. '1 are produced. Equalization of adjacent harmonics insures that the zero crossings of Fig. 6 are equally spaced and hence that the impulses of Fig. 7 will also be evenly spaced.

' The high frequency components of Fig. 7 passed to tube 49 are shown by Fig. 8. The selective amplifier tube 49 produces a steady 60 cycle tone from the impulses of Fig. 8 as shown in Fig. 9. The stability and equality of zero points of the wave of Fig. 9 is improved by the undesired harmonic equalizing condition described above.

It has been found that this method of selecting a desired harmonic and minimizing the disturbing effect of undesired harmonics permits frequency multiplication steps approximately double those possible with selective circuits tuned exactly to the desired harmonic.

This system has been used and found to be highly stable when the received impulses have a fundamental frequency of 31/3 cycles per second, the first selective feed-back amplier produces 20 cycles and the second produces 60 cycles. Transient effects in the system are almost entirely absent due to the use of aperiodic circuits@- limited to triodes. The number of limiter stages and the number of selective stages is not limited,

to two or to the same number of each. In some cases of frequency multiplication, a single har-v -monic equalizing selective feed-back stage may be sulcient for deriving a desired harmonic from a number of harmonics.

While one particular system has been shown for carrying out the present invention, many modifications are possible within the spirit and scope of the invention, as set forth in the appended claims.

What is claimed is: A

1. InA a system for operating a. synchronizable motor from a source of signal impulses, the combination of, an amplitude limiting device for equalizing the amplitudes of said signal impulses, an aperiodic' selective circuit for selecting a rst desired component from said equalized impulses, a second amplitude limiting device for equalizing said selected first desired component, a second aperiodic selective circuit for selecting a second desired component from said last equalized component, an amplifier for amplifying said second selected component, ancla circuit for applying said amplified component to said motor to control the speed of said motor in predetermined relation to signal impulses.

2. In a system for -operating a synchronizable motor from a source of synchronizing impulses, the combination of, an amplitude limiting device for equalizingthe amplitudes of said impulses, an aperiodic selective amplifier for deriving a substantially sinusoidal signal wave of predetermined frequency from said impulses, and an amplifier for amplifying said signal wave sufficiently to operate said motor therefrom.

3. In a system foroperating a synchronizablev motor from a source of synchronizing impulses,

lthe combination of, an amplitude limiting device for equalizing the amplitudes of said impulses, an aperiodic selective amplifier for deriving a substantially sinusoidal signal wave of a higher frequency from said impulses, and an amplifier for 5. The metnod'cf operating a tuname harmonic wave selector selecting a desired harmonic from" a group of uniformly spaced harmonics in which said desired harmonic lies midway between two 4undesired harmonics of unequal amplitude in conjunction with an amplitude limiter which inamplifying said signal wave sumciently to operate said motor therefrom.

4. 4'Ihe method of operating a tunable harmonic selector selecting a desired harmonic from a group of uniformly spaced harmonics in which undesired harmonics adjacent to said desired harmonic are of unequal amplitude for minimizing the eiiects of undesired harmonics which includes tuning said selector slightly off the desired harmonic in the direction of the lesser oi' two adjacent undesired V`harmonics on either Side of said desired harmonic. i

`cludes tuning said selector slightly oi the desired harmonic in the direction of the lesser of said two adjacent harmonics and afterward passing said selected harmonic thru said limiter.

6. In a system for operating a synchronizable electric motor under control of impulses derived from a source of synchronizing signals, the combination of, a thermionic vacuum tube with a resistor in series with one of its elements for equalizing the amplitudes of said signals, an amplifier including a resistance-capacity feed-back network for controlling the frequency characteristics amplitude of said amplifier for deriving a signal wave of a'` frequency adapted to operate said motor, and a second amplifier for amplifying said signal wave suiiiciently to operate said motor synchronously therefrom.

7. In a system for operating a synchronizable motor under speed control of a series 'of substantially equally spaced impulses, the combination of, a thermionic vacuum tube and. associated circuit for deriving constant amplitude unidirectional signals from said impulses, a second thermionic vacuum tube and an associated feed-back circuit for selecting a desired harmonic from said unidirectional signals, a thermionic vacuum tube amplifier for generating suflicient power to operate said motor synchronously with said harmonic, and va. circuit for applying said power to said motor. 8. The method of operating a tunable harmonic selector selected a desired harmonic from a group of uniformly spaced harmonics in which the selector is tuned slightly oif the desired harmonic to a higher frequency to minimize the eifects of the undesired harmonics on the waveform of the selected harmonic.

9. In a system for operating a synchronizable motor from a source oi synchronizing impulses. means for selecting a desired harmonic of said impulses for operating said motor wherein the selecting means has a maximum response at a frequency higher than the frequency lof said desired harmonic.

10. In a system for operating a synchronizable motor from a source of synchronizing impulses made up of a fundamental and a plurality ofharmonic components of decreasing magnitude a vselective circuit for selecting a desired harmonic 

